A vulnerability in the detection engine of Cisco Firepower System Software could allow an unauthenticated, remote attacker to bypass a configured file action policy to drop the Server Message Block (SMB) protocol if a malware file is detected. The vulnerability is due to how the SMB protocol handles a case in which a large file transfer fails. This case occurs when some pieces of the file are successfully transferred to the remote endpoint, but ultimately the file transfer fails and is reset.

An attacker could exploit this vulnerability by sending a crafted SMB file transfer request through the targeted device. An exploit could allow the attacker to pass an SMB file that contains malware, which the device is configured to block. This vulnerability affects Cisco Firepower System Software when one or more file action policies are configured, on software releases prior to 6.2.3.

Cisco Bug IDs: CSCvc20141.